package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;

import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermDocs;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.Explanation.IDFExplanation;
import org.apache.lucene.util.ReaderUtil;
import org.apache.lucene.util.ToStringUtils;

/** A Query that matches documents containing a term.
  This may be combined with other terms with a {@link BooleanQuery}.
  */
public class TermQuery extends Query {
    private Term term;

    private class TermWeight extends Weight {
        private final Similarity similarity;
        private float value;
        private float idf;
        private float queryNorm;
        private float queryWeight;
        private IDFExplanation idfExp;
        private final Set<Integer> hash;

        public TermWeight(Searcher searcher) throws IOException {
            this.similarity = getSimilarity(searcher);
            if (searcher instanceof IndexSearcher) {
                hash = new HashSet<Integer>();
                IndexReader ir = ((IndexSearcher) searcher).getIndexReader();
                final int dfSum[] = new int[1];
                new ReaderUtil.Gather(ir) {
                    @Override
                    protected void add(int base, IndexReader r) throws IOException {
                        int df = r.docFreq(term);
                        dfSum[0] += df;
                        if (df > 0) {
                            hash.add(r.hashCode());
                        }
                    }
                }.run();

                idfExp = similarity.idfExplain(term, searcher, dfSum[0]);
            } else {
                idfExp = similarity.idfExplain(term, searcher);
                hash = null;
            }

            idf = idfExp.getIdf();
        }

        @Override
        public String toString() {
            return "weight(" + TermQuery.this + ")";
        }

        @Override
        public Query getQuery() {
            return TermQuery.this;
        }

        @Override
        public float getValue() {
            return value;
        }

        @Override
        public float sumOfSquaredWeights() {
            queryWeight = idf * getBoost(); // compute query weight
            return queryWeight * queryWeight; // square it
        }

        @Override
        public void normalize(float queryNorm) {
            this.queryNorm = queryNorm;
            queryWeight *= queryNorm; // normalize query weight
            value = queryWeight * idf; // idf for document
        }

        @Override
        public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
            // only use the early exit condition if we have an atomic reader, because Lucene 3.x still supports non-atomic readers here:
            if (hash != null && reader.getSequentialSubReaders() == null && !hash.contains(reader.hashCode())) {
                return null;
            }

            TermDocs termDocs = reader.termDocs(term);

            if (termDocs == null)
                return null;

            return new TermScorer(this, termDocs, similarity, reader.norms(term.field()));
        }

        @Override
        public Explanation explain(IndexReader reader, int doc) throws IOException {

            ComplexExplanation result = new ComplexExplanation();
            result.setDescription("weight(" + getQuery() + " in " + doc + "), product of:");

            Explanation expl = new Explanation(idf, idfExp.explain());

            // explain query weight
            Explanation queryExpl = new Explanation();
            queryExpl.setDescription("queryWeight(" + getQuery() + "), product of:");

            Explanation boostExpl = new Explanation(getBoost(), "boost");
            if (getBoost() != 1.0f)
                queryExpl.addDetail(boostExpl);
            queryExpl.addDetail(expl);

            Explanation queryNormExpl = new Explanation(queryNorm, "queryNorm");
            queryExpl.addDetail(queryNormExpl);

            queryExpl.setValue(boostExpl.getValue() * expl.getValue() * queryNormExpl.getValue());

            result.addDetail(queryExpl);

            // explain field weight
            String field = term.field();
            ComplexExplanation fieldExpl = new ComplexExplanation();
            fieldExpl.setDescription("fieldWeight(" + term + " in " + doc + "), product of:");

            Explanation tfExplanation = new Explanation();
            int tf = 0;
            TermDocs termDocs = reader.termDocs(term);
            if (termDocs != null) {
                try {
                    if (termDocs.skipTo(doc) && termDocs.doc() == doc) {
                        tf = termDocs.freq();
                    }
                } finally {
                    termDocs.close();
                }
                tfExplanation.setValue(similarity.tf(tf));
                tfExplanation.setDescription("tf(termFreq(" + term + ")=" + tf + ")");
            } else {
                tfExplanation.setValue(0.0f);
                tfExplanation.setDescription("no matching term");
            }
            fieldExpl.addDetail(tfExplanation);
            fieldExpl.addDetail(expl);

            Explanation fieldNormExpl = new Explanation();
            byte[] fieldNorms = reader.norms(field);
            float fieldNorm = fieldNorms != null ? similarity.decodeNormValue(fieldNorms[doc]) : 1.0f;
            fieldNormExpl.setValue(fieldNorm);
            fieldNormExpl.setDescription("fieldNorm(field=" + field + ", doc=" + doc + ")");
            fieldExpl.addDetail(fieldNormExpl);

            fieldExpl.setMatch(Boolean.valueOf(tfExplanation.isMatch()));
            fieldExpl.setValue(tfExplanation.getValue() * expl.getValue() * fieldNormExpl.getValue());

            result.addDetail(fieldExpl);
            result.setMatch(fieldExpl.getMatch());

            // combine them
            result.setValue(queryExpl.getValue() * fieldExpl.getValue());

            if (queryExpl.getValue() == 1.0f)
                return fieldExpl;

            return result;
        }
    }

    /** Constructs a query for the term <code>t</code>. */
    public TermQuery(Term t) {
        term = t;
    }

    /** Returns the term of this query. */
    public Term getTerm() {
        return term;
    }

    @Override
    public Weight createWeight(Searcher searcher) throws IOException {
        return new TermWeight(searcher);
    }

    @Override
    public void extractTerms(Set<Term> terms) {
        terms.add(getTerm());
    }

    /** Prints a user-readable version of this query. */
    @Override
    public String toString(String field) {
        StringBuilder buffer = new StringBuilder();
        if (!term.field().equals(field)) {
            buffer.append(term.field());
            buffer.append(":");
        }
        buffer.append(term.text());
        buffer.append(ToStringUtils.boost(getBoost()));
        return buffer.toString();
    }

    /** Returns true iff <code>o</code> is equal to this. */
    @Override
    public boolean equals(Object o) {
        if (!(o instanceof TermQuery))
            return false;
        TermQuery other = (TermQuery) o;
        return (this.getBoost() == other.getBoost()) && this.term.equals(other.term);
    }

    /** Returns a hash code value for this object.*/
    @Override
    public int hashCode() {
        return Float.floatToIntBits(getBoost()) ^ term.hashCode();
    }

}
